During oil and gas well drilling and workover operations, precautions must be taken to prevent high pressure from the earth formations from escaping. Blowout preventer assemblies often include pipe rams, each having a packer element within. When the rams are brought together, the force causes the elastomer in the packers to seal around the pipe.
Some rams are configured to seal around a particular diameter of pipe. Others are variable in inner diameter in order to seal around a range of pipe diameter sizes. A typical variable ram packer has a central elastomeric body with a semi-cylindrical recess for receiving a pipe. Wings may extend radially outward from the central body. Each wing has a flat face that abuts against the flat face of one of the wings of the packer in the other ram.
Metal inserts embedded in the elastomer extend around the cylindrical recess. Each insert typically has upper and lower plates joined by a web. Metal wing top plates bond to the upper side of each wing, and metal wing bottom plates bond to the lower side of each wing. In the prior art, the portion of each top and bottom wing plate in contact with the elastomer of the wing bonds to the elastomer. The bonding is caused by applying adhesive coatings to these surfaces before placing the top and bottom wing plates in the mold.
As the packers seal around a pipe, the elastomer deforms and the inserts move. The bonding of the top and bottom wing plates can cause considerable strain in the elastomer as the bonded portions are not free to move relative to the top and bottom wing plates.
Also, strain occurs to the wing faces after sealing engagement. The high pressure differential of the well bore fluid being sealed can tend to break down the elastomer at the wing faces. High temperatures can increase the break down. The well bore fluid being sealed tends to flow upward from the lower to the upper side of the packers if the pressure is higher below.